The most common design for a flapper seal places the o-ring seal in a surrounding groove in a seat and allows a flapper having a conforming shape to land squarely on the o-ring seal while using the surrounding groove for seal support. Such a groove is shown in FIG. 9 of US Publication 2010/0314571. A modified form of this basic design is shown in FIG. 2 as item 34 in U.S. Pat. No. 4,478,286. Other designs deploy engaging outcroppings to protect the seal from the moving flow tube and which engage each other when the flapper seats off, as shown in FIGS. 7 and 8 of US Publication 2012/0012202. Other designs such as FIG. 2 of U.S. Pat. No. 7,841,416 use an edge-supported seal 70 that has a tapered shape in section and that has an end that is squarely engaged by the flapper 10. FIG. 11 in U.S. Pat. No. 6,666,271 shows a flapper landing a tapered edge squarely on a soft seat 80 and then if the pressure differential is higher the flapper 18 advances to the hard seat 50. Also of general sealing interest is U.S. Pat. No. 4,921,258 that shows a notch in the sealing element that receives a protruding member 58 to spread out a cantilevered end of the seal into sealing contact with a surrounding member 14. Curved flappers as shown generally in U.S. Pat. No. 5,682,921.
Sealing a flapper becomes more problematic with the designs discussed above at low pressure differentials. The designs that squarely engage the o-ring in low pressure situations do not bear on the o-ring with enough force to ensure proper sealing. In an effort to enhance the seal that is needed at low pressure differentials, the present invention provides a recess in the flapper preferably at its periphery such that only partial contact with the o-ring seal is obtained. This partial contact displaces part of the o-ring out of the groove in the seat such that an edge of the recess digs into the o-ring seal to compress an extending portion of the o-ring against the edge of the groove for fixation and sealing in low differential pressure environments. These and other aspects of the present invention will be more readily apparent to those skilled in the art by a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.